Make in-page callback survive navigations

This patch makes in-page callbacks survive navigations via
running in-page harness code on page load.

test/test.js

@@ -1,6 +1,9 @@
+var path = require('path');
 var Browser = require('../lib/Browser');
 
-describe('Page', function() {
+var EMPTY_PAGE = 'file://' + path.join(__dirname, 'assets', 'empty.html');
+
+describe('Puppeteer', function() {
     var browser;
     var page;
 
@@ -29,6 +32,30 @@ describe('Page', function() {
         var result = await page.evaluateAsync(() => Promise.resolve(8 * 7));
         expect(result).toBe(56);
     }));
+
+    describe('Page.setInPageCallback', function() {
+        it('should work', SX(async function() {
+            await page.setInPageCallback('callController', function(a, b) {
+                return a * b;
+            });
+
+            var result = await page.evaluate(function() {
+                return callController(9, 4);
+            });
+            expect(result).toBe(36);
+        }));
+        it('should survive navigation', SX(async function() {
+            await page.setInPageCallback('callController', function(a, b) {
+                return a * b;
+            });
+
+            await page.navigate(EMPTY_PAGE);
+            var result = await page.evaluate(function() {
+                return callController(9, 4);
+            });
+            expect(result).toBe(36);
+        }));
+    });
 });
 
 // Since Jasmine doesn't like async functions, they should be wrapped